1. Technical Field
This invention relates to a nonwoven web of synthetic fiber. In one aspect, this invention relates to a nonwoven web ofxe2x80x94absorbent fiber. In one aspect, this invention relates to a method of preparing a nonwoven web of superabsorbent fine synthetic fiber.
2. Background
Certain polymers are termed superabsorbent polymers for their ability to take up and hold fluids. Poly(acrylic acid) copolymer is one example of such a superabsorbent polymer.
Dry spinning can form superabsorbent polymer into continuous filaments. Dry spinning extrudes an aqueous solution of the polymer into air. Using a highly concentrated polymer solution, liquid filaments are extruded and then solidified, dried, hot-drawn, and heat-treated in a gaseous environment.
A nonwoven superabsorbent fibrous web can be produced by first forming an aqueous fiber-forming polymer solution into filaments which are contacted with a primary air stream having a velocity sufficient to attenuate the filaments. The attenuated filaments are contacted in a fiber-forming zone with a secondary air stream having a velocity effective to attenuate the filaments further, to xe2x80x9cfragmentxe2x80x9d the filaments into fibers, and to transport the fibers to a web-forming zone. The xe2x80x9cfragmentedxe2x80x9d fibers are collected in a reticulated web formed in the web-forming zone, and the web is cured.
A nonwoven fabric of water-soluble resin fibers can consist of water-soluble resin fine fibers having a mean fiber diameter of 30 xcexcm or less and a basis weight of 5 to 500 g/m2. The fabric can be produced by extruding an aqueous solution of water-soluble resin or a water-soluble resin melt plasticized with water through nozzles, stretching the extruded material to form fibers by a high speed gas flow, heating the fibers to evaporate the water in the fibers, and then collecting the fibers. The water-soluble resins can include poly(vinyl alcohol) when the application is directed primarily to the use of pullulan, a natural glucan. The high speed gas flow can consist of air at a temperature of from 20xc2x0 C. to 60xc2x0 C. at a linear velocity of 10 to 1,000 m/sec. The fibers can be dried by banks of infrared heaters located on both sides of and parallel to the fiber stream.
Some methods of forming fibrous webs or products from a solution of a polymer or molten polymer produce very short fibers and, consequently, differ significantly from meltblowing or spunbonding processes which can be used to prepare nonwoven webs from molten thermoplastic polymers.
Steam can be used in the fiber-forming process. A water-containing polymeric composition can be extruded under conditions using a supercritical fluid solution, preventing flashing, and spraying water-imbibed gelled fibers to form webs.
Meltblowing can be used in the fiber-forming process.
Coforming can be used in the fiber-forming process. Fibers or particles are commingled with meltblown fibers as they are formed.
Spunbonding can be used in the fiber-forming process.
Superabsorbent precursor polymers having high molecular weights, e.g., by way of example, molecular weights higher than 500,000, and minimum cross linkage can provide high fluid absorbency under load.
By superabsorbent polymer is meant a polymer which can provide high fluid absorbency under load at a level of 10 grams of 0.9% by wt. aqueous sodium chloride per gram of dry absorbent fiber or nonwoven web.
Spinning fiber from high molecular weight polymers is very challenging, even in the case where the polymer is a linear chain polymer, particularly when the molecular chain is flexible.
Ultra high modulus and high strength fibers from extremely high molecular weight polyethylene are prepared only by a slow gel spinning.
Fiber spinning from a solution of a linear chain, flexible polymer involves un-entangling and stretching of coiled and entangled polymer molecules in the solution. When these molecules are large, the process of un-entangling and stretching becomes very difficult and slow, if successful at all. The relaxation time is long.
U.S. Pat. No. 5,280,079 discloses a method of making a substantially linear acrylic polymer having a hydroxy alkyl ester comonomer. The linear polymer can be shaped into fiber, film, or coating before crosslinking occurs. However, because of the nature of esterification reaction, crosslinking initiation requires extremely high temperature (i.e., 200xc2x0 C.) and takes a long period of time. In commercial practice, the method is impossible for a continuous process, especially when a continuous roll-form non-woven material is preferred.
Preparing substantially continuous fiber from a solution of high molecular weight polymer has been thought to be impossible particularly with high speed nonwoven spinning processes. The high speed nonwoven spinning process is operated at spinning speeds 10 times to 100 times higher than in the conventional textile fiber spinning. At the higher spinning speeds, micro-fiber web from high molecular weight (124,000-180,000) poly(vinyl alcohol) was observed to become shoty, indicating fiber breakage.
It is an object of the present invention to provide a novel nonwoven web and method of preparing a preferred nonwoven web including substantially continuous superabsorbent microfiber having mechanical strength, high fluid absorbency, and preferred handling properties.
It is an object of the present invention to provide a novel nonwoven web and method of preparing a novel and preferred nonwoven web including continuous superabsorbent fine fiber having mechanical strength, high fluid absorbency, and preferred handling properties.
Another object of the present invention is to provide novel and preferred substantially continuous superabsorbent microfiber and a nonwoven web including microfibers having mechanical strength, high fluid absorbency, and preferred handling properties.
A further object of the present invention is to provide preferred continuous superabsorbent fine fiber and nonwoven webs including fine fibers having mechanical strength, high fluid absorbency, and preferred handling properties.
Still another object of the present invention is to provide a disposable absorbent product which includes a preferred nonwoven web including substantially continuous superabsorbent microfiber.
Yet another object of the present invention is to provide a disposable absorbent product which includes a preferred nonwoven web including continuous superabsorbent fine fiber.
These and other objects will become apparent further from a consideration of the detailed description of the specification and the figures of the drawings which follow.
The present invention provides a synthetic fibrous nonwoven web and method of preparing a novel nonwoven web of synthetic fiber. An aqueous solution of synthetic precursor polymer containing an amino functional group is extruded under defined conditions through a plurality of die orifices to form a plurality of threadlines. The threadlines are attenuated with a defined primary gaseous source to form fiber under conditions of controlled macro scale turbulence and under conditions sufficient to permit the viscosity of each threadline, as it leaves a die orifice and for a distance of no more than about 8 cm, to increase incrementally with increasing distance from the die, while substantially maintaining uniformity of viscosity in the radial direction, at a rate sufficient to provide fiber having the desired attenuation and mean fiber diameter without significant fiber breakage. The attenuated threadlines are dried with a defined secondary gaseous source. The resulting fibers are deposited randomly on a moving foraminous surface to form a substantially uniform web. The moving foraminous surface is positioned about 10 to about 100 cm from the last gaseous source to contact the threadlines. The fibers have a mean fiber diameter in the range of about 0.1 to 30 xcexcm and are substantially free of shot. The attenuating and drying steps are carried out under conditions of controlled macro scale turbulence.
The superabsorbent fiber nonwoven webs of the present invention are useful in the production of disposable absorbent products. The superabsorbent fiber nonwoven webs of the present invention are useful particularly in the production of diapers, training pants, catamenial devices, sanitary napkins, tampons, incontinent products, and tissue wipes.